Although the precise role of CSF-1 in mature osteoclast function is not known, we have shown that CSF-1 is a potent chemoattractant for osteoclasts. Activated c-fms, the receptor for CSF-1, associates with and activates, P13-kinase (P13-K), a multifunctional lipid kinase that plays an important role in signal transduction. A growing body of evidence suggests an integral role for P13-K in mediating CSF-1-induced ruffled border formation, motility, resorption and osteopontin-induced actin polymerization in osteoclasts. We have shown that inhibition of P13-K with the non-isoform specific inhibitors wortmannin and LY294002, completely abrogates CSF-1-induced cytoskeletal remodeling in osteoclasts. Distinct downstream responses to CSF-1 in macrophages are mediated by different isoforms of Class Ia P13-Ks. The p110delta isoform, in particular, appears to be critical for CSF-1-induced macrophage migration and actin/cytoskeletal reorganization. To date, few data are available about the expression and regulation of P13-K isoforms in osteoclasts, although recent studies from our lab demonstrate that p110delta and p110alpha are expressed in osteoclasts. We propose to explore the expression of the different PI3-K isoforms in osteoclasts, and to characterize the effect of CSF-1 on the activation and cellular distribution of these isoforms. Using immunocytochemical and confocal microscopy, we will examine the effect of CSF-1 on the subcellular distribution and redistribution of these isoforms. Using antibodies to the specific isoforms, we will investigate the effect of blockade of individual isoforms on spreading, motility, and resorptive activity in osteoclasts. In the aggregate these studies will refine our understanding of the role of P13-kinase in CSF-1 actions in osteoclasts and potentially identify new targets for drug discovery.